Internal combustion engines use timing chain drive systems which comprise a chain and sprockets. Example chain configurations known in the art include; inverted teeth (IT) chains, bush chains and roller chains. Due to the impact of the chain on the sprocket during meshing, the chain generates vibration and noise. Due to the uniform distribution of the sprocket teeth along the sprocket perimeter, vibration and noises occur at fundamental meshing frequency and this frequency is in positive integer multiples. The fundamental meshing frequency for a single loop timing chain in Hertz is given by the formula:v=(nengine/60)×zcrank wherein nengine is the engine angular velocity in rpm and zcrank is the crankshaft sprocket number of teeth.
Conventionally, in order to reduce noise and vibration, the uniform teeth distribution of the sprocket teeth around the sprocket perimeter is altered and hence the time interval between two consecutive impacts are unequal. This breaks the uniform pattern and hence the noise and vibrations are spread around a broader spectrum of frequencies while the amplitude of the meshing orders are decreased and eventually masked by the engine noise generated by source other than the chain meshing. An attenuation of the unpleasant meshing pure tones is expected but not necessarily a decrease of the overall noise and vibration level.